The present invention relates generally to protection switching techniques in communications networks, and more specifically to a protection switching technique that makes more efficient use of network resources.
In recent years, Internet Service Providers (ISPs) and operators of communications networks have increasingly employed protection switching techniques to enhance the level of survivability of the networks in the event of a fault caused by, e.g., the failure of a node in the network, the failure of a link interconnecting network nodes, or a switchover condition. By employing such protection switching techniques, ISPs and operators of communications networks seek to assure fast recovery from network faults with minimal disruption to traffic flow on the network.
A conventional protection switching technique, commonly known as 1+1 protection switching, requires the provision of both a “working” communications path and a “protect” communications path between a pair of nodes in a communications network. For example, the working path and the protect path may be provided between a source node and a sink node in a “protected” domain of the communications network. Further, the working path and the protect path may include respective pluralities of nodes interconnected by respective communications links.
In the 1+1 protection switching technique, the source node receives incoming data traffic and sends outgoing data traffic to the sink node over both the working path and the protect path simultaneously. In the event the working path is in a fault-free condition, the sink node selectively receives the data traffic provided over the working path and ignores the data traffic carried by the protect path. In the event of a fault in the working path caused by, e.g., a node/link failure or a switchover condition, the sink node receives notification of (or otherwise identifies) the fault and subsequently selects the data traffic carried by the protect path. Because the sink node can select the data traffic on the protect path as soon as it identifies the fault on the working path, the 1+1 protection switching technique allows fast recovery from node or link failures in communications networks with minimal disruption to the data traffic carried by the network.
However, the 1+1 protection switching technique has drawbacks in that at least twice the amount of bandwidth must be reserved for sending the data traffic from the source node to the sink node than would normally be required for data transmission without such protection switching. This results in inefficient use of network resources and increases in the overall complexity and cost of the communications network.
Another conventional protection switching technique, commonly known as 1:1 protection switching, also requires the provision of a working communications path and a protect communications path between a source node and a sink node in a communications network. However, instead of sending outgoing data traffic to the sink node over both the working and protect paths simultaneously as in the 1+1 protection switching technique, the 1:1 protection switching technique only requires the source node to send “protected” data traffic to the sink node over the working path. In the event the working path is in the fault-free condition, the source node may also send “unprotected” data traffic over the protect path to the sink node, which may subsequently receive both the protected and unprotected data traffic provided over the working and protect paths, respectively. In the event of a fault in the working path or a switchover condition, the source node sends the protected data traffic to the sink node over the protect path instead of the working path and discards the unprotected data traffic.
Because the additional bandwidth provided by the protect path is used for sending unprotected data traffic to the sink node when the working path is in the fault-free condition, the 1:1 protection switching technique generally makes more efficient use of network resources than the 1+1 protection switching technique. However, the 1:1 protection switching technique also has drawbacks in that when there is a fault in the working path, the recovery from the fault causes minimal disruption to the protected data traffic but allows the unprotected data traffic to be lost.
It would therefore be desirable to have a protection switching technique that can be employed to enhance the level of survivability of a communications network in the event of a fault. Such a protection switching technique would make more efficient use of resources in the communications network. It would also be desirable to have a protection switching technique that reduces the loss of data traffic carried by the network.